The invention relates to microsystems adapted to handle suspended particles or biological cells, in particular ot the configuration of electrodes for dielectrophoretic deflection of particles or cells, and applications of such microsystems.
Known in the art is to manipulate fluid-suspended particles in microsystems with electrode-channel-arrangements based upon negative or positive dielectrophoresis, wherein polarization forces are generated during exposure to high-frequency electrical fields, enabling a repulsion from the electrodes and, in conjunction with flow forces in the suspension fluid, making it possible to manipulate the particles in the microsystem. An overview of known microsystem is given e.g. by G. Fuhr et al. in xe2x80x9cNaturwissenschaftenxe2x80x9d, Volume 81, 1994, p. 528.
Conventional microsystems have disadvantages relating to the stability and life time of the electrodes, and a limitation to specific potential forms corresponding to the respective electrode geometry.
The microelectrodes of conventional microsystems generally exhibit straight bands, which are oriented in a certain way relative to the channel to achieve specific field barriers in the channel of a microsystem. Mechanical stresses, material fatigue, or production defects can lead to breaks in the straight electrode bands, and hence cause a malfunction of the entire microsystem. In addition, a conventional system is limited to a specific function corresponding to the given electrode structure. Variable actions for particle deflection in a given microsystem are not possible.
A microsystem for dielectrophoretic sorting of particles and cells is known from the publication of S. Fiedler et al. in xe2x80x9cAnal. Chem.xe2x80x9d vol. 70, 1998, p. 1909. The microsystem contains an electrode arrangement with a plurality of strip shaped, triangular or rectangular electrodes.
Consideration is now being given to ways of improving electrode arrangements for microsystems with dielectrophoretic particle deflection to overcome the disadvantages of conventional microsystems. Attention is also directed towards indentifying or developing applications for the improved electrode arrangements.
In accordance with the present invention, provides a new microsystem adapted for the dielectrophoretic manipulation of particles in a suspension fluid in a channel. The microsystem contains an electrode arrangement with at least one electrode arranged on a lateral wall of the channel. The electrode has plurality of electrode segments facing the channel for generating field gradients. The electrode segments are formed by portions or areas of a metal coating which are exposed to the channel through recesses in an insulating layer that coats the metal coating.
The basic idea underlying the invention is, with an electrode arrangement of a microsystem with dielectrophoretic particle deflection consisting of at least one electrode, to divide the electrode into electrode segments. The electrode segments are set up to be exposed to potentials jointly or separately and, working together, to generate a field barrier corresponding to the function of the respective electrode in the microsystem. The electrode segments are electrode surfaces exposed relative to a fluid in the microsystem, which surfaces are electrically connected as a function of application, wherein the areas of the electrical connections are not exposed relative to the fluid in the microsystem, i.e., are covered or electrically isolated from each other. The transition from conventional, planar-shaped or band electrodes to the electrode segments according to the invention advantageously solves the above object from a variety of standpoints. On the one hand, the electrode segments are less susceptible to faults, as will be explained in detail below. On the other hand, with separate actuation, they permit a multiple functionality of the microelectrodes, and hence of the microsystems themselves, that is not provided in conventional microsystems.
In a first embodiment, the electrode segments are formed by electrodes with a planar or band expansion carrying an insulation layer, which has recesses in predetermined sections. The recesses exhibit the shape and position of the desired electrode segments. Through the recesses, the fluid in the microsystem contacts the electrode, which only becomes active via the recesses or electrode segments due to the insulating or dielectric cover, and is otherwise inactive. This configuration is advantageous for the life time of the electrodes, since even a break off of the entire electrode part open to the fluid will not cause the electrode to fail.
In a second embodiment of the invention, the electrode segments are individually actuatable, independently from each other. The electrode segments that together assume an electrode function are arranged in the microsystem, e.g., along a channel wall, in an area shaped like a conventional electrode that would be provided for performing this function. The electrode segments can be separately exposed to potentials that vary by application relative to the phase position and amplitudes.
In another embodiment of the invention, electrode segments electrically isolated from each other and individually actuatable are arranged as an electrode array. An electrode array consists of numerous point or planar electrode segments, arranged e.g. like a matrix in rows and columns or in other geometric configurations depending on application, of which a predetermined number of electrode segments are exposed with electrical potentials to produce a specific electrode function during the operation of the microsystem, while the remaining electrode segments of the electrode array are not actuated. This is a particularly advantageous configuration of an electrode arrangement according to the invention, since the electrode segments can be differently actuated depending on application, and hence the electrode function can be freely selected. As will be explained below, this function selection can take place irreversibly or reversibly.
Other important aspects of the invention include the geometric configuration of electrode segments, with which gradients, and hence varyingly strong forces can be generated, and/or which are adjusted to the flow profile in the suspension fluid. The advantage to the latter configuration is that the electrodes can be shorter in design, and are exposed to lower forces, while still exhibiting the identical effectiveness as conventional microelectrodes.
Preferred applications of the invention lie in techniques in fluid microsystems for separating, manipulating, charging, fusing, permeating, pairing and aggregating microscopically small, suspended particles (synthetic particles and/or biological particles, e.g., biological cells, cell constituents or macromolecules).
In a special embodiment of the invention, the particles are moved in a microsystem with electrode forms designed conventionally or in accordance with the invention during exposure to centrifugal and/or gravitational forces.
Further features of the invention, its nature and various advantages will become more apparent from the accompanying drawings and the following detailed description.